Jet engine protection system

ABSTRACT

A modern jet engine inlet protection system that protects against large birds and operates autonomously, that is dormant in routine aircraft operations, that automatically actuates its protective device(s) only at the immediate point of need, then returning it (them) to a non-interfering position, including a RADAR system and a LIDAR system which detect birds entering the intended flight path of the aircraft, and fast computer-implemented computational algorithms that track and identify those from the detected set that are (1) projected to enter a zone which would lead to ingestion by the engine, and (2) of a size large enough that they would seriously damage the engine if ingested; that includes defensive mechanisms housed in the engine nacelle cowling or center hub, or in the fuselage structure that are instantaneously actuated shortly before arriving at the point of impact to shield, deflect, reduce the size of the approaching bird to an acceptable mass, or destroy it, and, that after the ingestion threat has passed, the devices are stowed/retracted or safely jettisoned.

CROSS REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. provisional patentapplication 61/218,825, filed Jun. 19, 2009, the entirety of which isincorporated by reference herein.

FIELD OF INVENTION

The invention relates generally to systems and methods for protectingjet engines from ingestion of foreign objects, such as large birds,during flight and an alternative embodiment specifically adapted forprotection of a vulnerable region of helicopters. More particularly thesystems relate to mechanical devices that function to mitigate the riskof bird strikes to aircraft engines.

BACKGROUND

There are many known systems and devices intended to protect jet enginesin general, and those on aircraft in specific. Nearly all employ sometype of shield in front of the inlet, and they have taken various formsand use a variety of means. As in many fields of endeavor, successivedevelopments are made but subsequently are found lacking as newunderstandings and problems arise out of often unintended consequences.A review of patents directed to such systems and devices confirms this,and also shows that one specific issue dominates. One central problem inthis field involves failed attempts to avoid a significant reduction inairflow that arises from the specific system or device being made.Several such designs claim to have solved this problem, but each of theproposed solutions brought with it some further complication, e.g., if aretractable shield was presented as the solution, the shield and relatedmechanisms became prohibitively complex and heavy.

Also, it is apparent that several of these prior attempted solutionswere based on premises that either no longer apply or were flawed. Onesuch assumption, used by certain designs, is that bird strikes occuronly in that portion of the flight at or when approaching an airport.While it is true that a large percentage of recent bird strikes haveoccurred there, a system designed to operate only in this flight regionleaves the aircraft vulnerable to bird strikes that can and do occur inall phases of flight, including at high altitude. Publicly availabledata show damage to aircraft from routine encounters with birds atflight altitudes of 10,000 feet and well above.

None of these known systems has found its way into practicalapplication. Also, nearly all are limited in application because theyhave potential use only for an older type of aircraft jet engine—theturbojet. Few relate to the situation and circumstances presented by thenewer engine design now widely in use on commercial aircraft—thehigh-bypass ratio turbofan—and those few contain significant problemsyet to be successfully addressed.

Since the time of the earliest patents in this field, inventors haveenvisioned affixing some type of metal screening structure in front ofthe engine intake for the general purpose of preventing the ingestion ofdebris. However, the preponderance of patents specifying this type ofscreen device recognizes that it causes problems. For example, U.S. Pat.No. 2,507,018, dating from 1950—only just over 10 years after the firstjet engine flew—was an annular inlet screen, inside the inlet duct,sloping forward from nacelle cowling to center hub, and made ofaerodynamically shaped metal slats attached to aerodynamically shapedstruts. This entire apparatus was to be electrically heated in anattempt to deal with ice buildup on the struts. Several patents followedthat provided alterations on the type and/or placement of the metalscreen system, and all dealt with the need for anti-icing.

To operate as designed, a jet engine needs to have a large quantity ofair flowing into the inlet, with the flow essentially undisturbed by anyobject encountered prior to entering the inlet. A problem not addressedby some early designs and that they created or contributed to was asignificant reduction in airflow caused by the blockage of the inlet bythe metal system. Later designs attempted various techniques to addressthis problem. For example, U.S. Pat. Nos. 3,196,598; 3,871,844;4,149,689; and 5,411,224 each address this problem with techniques suchas placing the screen in front of the inlet and making it a very largeoval- or cone-shaped apparatus when viewed from the side, and shapingthe screen material into a sort of airfoil cross-section, with theintent of reducing inlet blockage.

Other designs proposed using a screen having movable members, allowingthe screen to be in a sort of retracted mode for what was considerednon-hazardous portions of the flight. However, such designs presentedseveral problems, including very complex mechanisms needed for movementbetween their stored and operational states. Also, although birds aremore likely to be encountered by aircraft during the lower altitudeflight departing or arriving at an airport, there have been manydamaging bird strikes in other flight regimes, and those designs do notprovide aircraft engine protection throughout the entire flightenvelope.

Three recent patent publications mention the modern turbofan jet engineor show a configuration on what is possibly a variant of a modern jetengine. U.S. Pat. No. 6,089,824 proposes a solution that instead ofplacing a screen across the inlet to prevent bird ingestion; acone-shaped, spinning cutter is attached to the rotating engine shaftout in front of the inlet, and is intended to dismember incoming birds.U.S. Pat. No. 6,138,950 describes a concept resembling that originallyemployed in the 1970s on one military aircraft—the Lockheed F-117A“Stealth Fighter”. In this implementation the inlet is covered with athick plate that forms a porous grid including a set of adjoining tubes.Several different aircraft are shown with the device, including oneinstallation on what resembles a turbofan engine. International patentpublication WO/2001/012506 describes a device that includes elementswhich can move between a first, inactive position in which the air inletis substantially open; and a second, active position in which theelements form the protection in front of the inlet opening.

Also, U.S. Pat. No. 7,494,522, corresponding to International patentpublication WO/2007/0245697 describes numerous designs, all of whichinvolve screens that are mostly inside the engine itself and attached toa rotating pole.

Bird strikes are becoming more frequent, though mainly they have notcaused catastrophic loss of aircraft and lives. The recent loss of acommercial aircraft to bird ingestion—although amazingly all thepassengers survived—has brought into sharp focus the reality of themassive increase in bird populations around the world, and especially inthe continental United States. Experts in the field have stated prior tothe accident referred to, that they had expected to lose aircraft tobird strikes. What they did not expect was that anyone wouldsurvive—much less the entire complement of occupants. Predictions arethat bird populations will continue to increase. Along with this hasbeen an increase in the mass (weight) of the birds and thus a higherpercentage of such birds being involved in bird strikes. All modern jetengines are designed to U.S. Federal Aviation Agency-mandatedrequirements that specify the type of continued operation afteringesting a bird of specified size, at a specified aircraft speed.Modern jet engines have demonstrated the ability to achieve thesespecified requirements in test environments. However, a real problemexists in that in actual, non-test conditions birds that collide withjet engines have at times weighed more than what the FAA-mandated weightrequirement specifies. While jet engine manufacturers have been able tooccasionally demonstrate in tests successful handling of a collisionwith a somewhat heavier bird than the FAA requirement, such tests havenot been consistently successful. As a result, large, heavy birdscurrently pose an unmanageable threat to commercial aviation safety.

Finally, turning to the modern turbofan jet engine, it is distinguishedby its very large inlet, far beyond the dimensions of the turbojetengine, for which nearly all of the earlier jet engine protectiondesigns were directed. The very size of this inlet challenges, if notrenders useless virtually all of these previously known engineprotection designs. Of those few that were intended for possible use ona turbofan jet engine, the inventors expressed concern about the crucialneed to avoid reducing engine performance. While attempts were made tosatisfy this objective, e.g. by having the engine protection systemremaining completely imbedded within existing structure until orderedinto play by some pilot action, none was designed to be completelyautonomous. Also, none was designed to operate in fractions of a second,none was able to determine the need for actuation based on accuratelyassessing the mass of the approaching bird, none employedbird-shielding, deflecting, or destructive mechanisms and none addressedprotection of the central region of the engine inlet, rather than theentire fan area, to prevent the ingested bird from travelling into thecore of the engine. It is the engine core that is susceptible tocomplete and unrecoverable engine failure from such ingestion. All theseproblems and concerns are addressed in the systems and methods describedherein.

SUMMARY

The engine protection system, for which multiple embodiments aredescribed herein, in its stored mode does not degrade aircraftperformance, deploys only when needed and is actuated in a timelyfashion in response to information it gathers about oncoming threats,primarily birds. They provide protective guards for jet aircraftengines, and improved methods for detecting, identifying, tracking, andpredicting the likelihood of collision with a protected engine bybird(s) of a size determined to require protecting against impact;determining the necessity of deploying the guard(s) against such bird(s)as opposed to maneuvering the airplane to avoid the bird entirely;actuating and deploying the protecting device(s), if it is determined todo so, in sufficient time to avert or deflect impact with the engine;and for retracting or safely disposing the device(s); all involving, butnot limited to, the modern high-bypass ratio turbofan jet engine, and toprotecting the exposed, vulnerable components of a helicopter rotorcontrol system against the specific threats listed above. In alternateembodiments they provide for automatically protecting the air intake ofa modern high-bypass ratio turbofan engine from the ingestion of birdsand other foreign objects. The preferred system is preferably housed inthe nacelle cowling or center hub of the turbine engine or fuselagestructure which, on actuation, expands to momentarily shield, deflect,reduce the size of the approaching bird or other foreign objects to anacceptable mass. Actuation is preferably commanded automatically,without requiring human decision or action, by a sub-system comprised ofa sensor which detects birds or other object entering the intendedflight path of the aircraft; fast computational algorithms that trackand identify those from the detected set that are projected to enter azone which would lead to ingestion by the engine, and of a size orweight large enough to seriously damage the engine if ingested. Afterthe ingestion threat has been disposed of, components of the system arestowed, retracted or safely jettisoned. The present systems providealternative embodiments for dealing with large birds and also protectingthe core engine region of the inlet. The present systems thus preventcertain foreign objects from entering the air intake of a jet turbineengine. Finally, the systems also include an alternative embodiment thatis specifically useful for and adapted to protection of a vulnerableregion on helicopters.

The systems relate to protective guards for jet aircraft engines,specifically to improved methods for detecting, identifying, tracking,and predicting the likelihood of collision with a protected engine bybird(s) of a size determined to require protecting against impact;determining the necessity of deploying the guard(s) against suchbird(s); actuating the protecting device(s) in sufficient time to avertor deflect impact with the engine; and for its retraction or safedisposal; all involving, but not limited to, the modern high-bypassratio turbofan jet engine, and to protection of the exposed, vulnerablecomponents of a helicopter rotor control system, against the specificthreats listed above.

These and other embodiments, features, aspects, and advantages of theinvention will become better understood with regard to the followingdescription, appended claims and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and the attendant advantages of the presentinvention will become more readily appreciated by reference to thefollowing detailed description, when taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a simplified schematic depicting the distributed components ofseveral embodiments of a preferred jet engine protection system;

FIG. 2 is a front view of a modern, conventional high-bypass ratioturbofan jet engine;

FIG. 3 is a simplified cross-sectional view of a modern, conventionalhigh-bypass ratio turbofan jet engine;

FIG. 4 is a simplified cross-sectional schematic view of a turbofan jetengine with a preferred mechanical embodiment defensive system installedin its stowed or retracted position inside the engine nacelle;

FIG. 5 is a simplified cross-sectional view of the FIG. 4 embodimentdepicting the defensive system in an active or extended position;

FIG. 6 is a simplified perspective view of the FIG. 4 embodiment shownin the extended position as shown in FIG. 5;

FIG. 6A is a side view of an alternate, biconvex shaped rod used in thedefensive system;

FIG. 6B is a cross-sectional view of the FIG. 6A rod, taken through line6B-6B of FIG. 6A;

FIG. 7A is a cross-sectional view of an alternate embodiment in whichthe active members are stored in the center hub of a modern,conventional jet engine and shown in their stowed position;

FIG. 7B is a cross-sectional view of the FIG. 7A embodiment but with theactive members in their extended or deployed position;

FIG. 8 is an isometric view of an alternate embodiment comprising ahigh-strength, inflatable fabric bag in an actuated position;

FIG. 9 is an isometric view of an alternate embodiment inflatable fabricbag having an alternate shape compared to the FIG. 8 embodiment, andwith the bag depicted in an actuated position;

FIG. 10 is a simplified schematic of an embodiment of the real-timecomputer program algorithm that can be used to assess the threat levelof the detected airborne object, such as a bird;

FIGS. 11A and 11B are schematic representations of an alternateembodiment, dynamic inflatable or morphing bag or device showing twostages of its deployment: a stage immediately after release from thenacelle (11A) and a stage in mid-deployment (11B);

FIGS. 12A and 12B are schematic representation of the FIGS. 11A and 11Bembodiment depicting two stages during one possible post-capturescenario, after the bird has been captured by the device (12A), and inwhich the device is jettisoned (12B);

FIGS. 13A and 13B are schematic representations of two stages duringoperation of an alternate embodiment depicting a bag as shown in FIGS.11A and 11B, but with an alternate structure for a post-capture scenarioin which the device is retained (13A) and held next to the nacelle(13B);

FIG. 14 is a front view of the FIGS. 11A and 11B embodiment seen duringits mid-deployment stage;

FIG. 15 is an isometric view of the FIGS. 11A and 11B embodiment seenduring its mid-deployment stage.

FIG. 16 is a schematic representation of a helicopter, illustrating thelocation of the blade control mechanism;

FIG. 17 is a second schematic representation of a helicopter, depictingan alternative embodiment aircraft protection system at the helicopterblade control mechanism location and with its protective metal structurein a stowed or retracted position;

FIG. 18 is a schematic representation of the FIG. 16 embodimentdepicting the protective metal structure in an active or extendedposition on the helicopter.

Reference symbols or names are used in the figures to indicate certaincomponents, aspects or features shown therein. Reference symbols commonto more than one figure indicate like components, aspects or featuresshown therein.

DETAILED DESCRIPTION

The jet engine protection systems described herein are directed topreventing serious damage to modern jet engines due to ingestion ofrelatively large birds or other objects. Two principal mechanicalsystems or sub-systems include a set of rods or tubes configured into acone-shaped arrangement upon deployment and, secondly, a deployableairbag-like device. These preferred embodiments function to reduce theseverity of an engine-bird impact by breaking up the bird or deflectingit altogether. Both of these systems or sub-systems preferably comprisea sensor sub-system, a threat level evaluation sub-system and anactuator sub-system. In general the sensor component or sub-systemdetects an oncoming object in the aircraft's flight path and then sendsdata signals to the evaluator, which typically is a digital computer ordigital processor, most preferably a real-time embedded softwareprogram. The evaluator determines the likelihood of the object'scollision with the aircraft and then generates output control signals toactuate the mechanical deterrent sub-system or device. These systems caninvolve and employ, in addition to well-developed materialstechnologies, modern conventional technologies such as bird detectionradar, miniaturized computers utilizing fast computational algorithms,components such as actuating mechanisms and materials from automobilecrash airbag systems, advanced reactive defensive system components,and, optionally, microwave technology or other directed energy methods.

The systems described herein are intended to protect a modern jet engineagainst relatively large birds or other objects which, if ingested wouldseriously damage or destroy the engine. The active components or membersof these systems are dormant during routine aircraft operations, andpreferably are automatically actuated only when an immediate need, i.e.,imminent collision arises. After use in flight, the active members arethen returned to their dormant, non-interfering position or disposed. Ingeneral, the overall system preferably includes a sensor sub-systemwhich detects birds entering the intended flight path of the aircraft;computer implemented fast computational algorithms that track andidentify such birds or objects from the detected set that are projectedto enter a zone which would lead to ingestion by the engine and are of asize large enough or weight great enough that they would seriouslydamage the engine if ingested, and a momentary defensive system, such asa mechanical guard device, a maneuver routine, or a directed energyemitter. Shortly before the detected obstacle is to arrive at the pointof impact, the momentary defensive system is turned on and actsinstantaneously to shield, deflect, reduce the size or destroy theapproaching bird so that it or its remains are reduced to mass that willnot cause serious damage to the engine. After the ingestion threat haspassed, the active devices are preferably stowed, retracted, safelyjettisoned, or deactivated.

In order to establish a broad range of useful applications the presentsystems are intended for and adapted for functioning in scenarios beyondexisting FAA regulations. In particular, FAA regulations FAR 25.631 and25.571(e) (1) mandate commercial aircraft empennage leading edgeresilience to bird strikes in an 8 pound weight class and below. Heavierbirds, such as geese pose a significant threat to both the airframe andthe engines. As seen in US Airways flight 1549's Hudson River landing,flocks of such birds pose an even greater threat, a threat that isoutside of currently mandated resilience.

Due to the severity of commercial airline-class accidents the presentsystems are most preferably adapted for use in such aircraft. One canconsider a representative 747-class aircraft encountering one or moreCanadian geese, which typically weigh more than 8 pounds, as a scenarioto which the present systems are addressed. Such an encounter couldoccur at almost any altitude. While high-altitude bird strikes are lesscommon, they have been confirmed at altitudes in excess of 30,000 feet.Based on historical data, about 41% of reported civil aircraft birdstrikes in the United States occur during take-off or landing. Inaddition, about 75% of all bird strikes occur at less than 500 feetabove ground level (AGL). During the 1990-2008 period more than 2,200bird strikes involving civil aircraft at heights above 5,000 feet AGLwere reported in the United States. It is believed that acommercially-viable system should offer protection in all of thesescenarios, and the nominal case of an encounter at cruise speed isconsidered for the reason that this poses the most stringentrequirements on the system.

Deployment Requirements

To understand the loads resulting from the impact of a bird, theduration of the collision event, sometimes referred to as the “squash-uptime”, must be determined. Experimental results show that this eventcommonly lasts 3-6 milliseconds. Based on the representative aircraftand bird type, the timing requirements for deployment of the system canbe determined. Suppose a 747-class aircraft is cruising at 555 miles perhour (48,840 feet per minute) and encounters a Canadian goose in itsflight path. If the bird is flying at 3,500 feet per minute and thesensor sub-system can detect its presence at a range of 0.5 miles, thenthe time between detection and collision would be approximately 3seconds. If a safety factor is included in the calculation, thedeployment time for the mitigation device would be no more than 1-2seconds. To meet this deployment requirement, damped pyro actuatorswould be suitable, as would be a linear actuator.

Sensor Sub-Systems

Conventional RADAR and LIDAR systems have the capability for performingthe sensor functions in the present systems and are therefore consideredto be preferred components in a sensor sub-system. As used in thiscontext the term LIDAR is intended to have its commonly understoodmeaning: a device that is similar in operation to radar but emits pulsedlaser light instead of microwaves. A LIDAR system similar to the RieglVQ-480 system has a beam footprint of approximately 9 inches in diameterat a distance of one-half mile (considered to be 2,600 feet). Toregister an object on this system, the target must be larger than thefootprint of the beam or consecutive scans must be made to overlap andthus to create an effectively smaller footprint. For a bird with afrontal silhouette of 12 inches in diameter, a conservative estimate fora Canadian goose, the LIDAR beam will easily register the target at thisdistance without needing to overlap scans. If the beam is swept acrossits 60 degree field of view, that is 90 feet above and below theaircraft, which is 2 degrees above and below the projected flight path,at a scan rate of 100 scans per second, it will take nearly 2.5 secondsto sweep across the entire area of interest. Because this scan time ison the same order as the time available for the nominal case deploymenttime, it is believed that a LIDAR based sub-system will functionsuccessfully as a sensor component or sub-system. LIDAR products withlonger detection ranges are already commercially available, and thistechnology is likely to advance in the coming years, further enhancingthe sensitivity of the system.

Referring to FIG. 1 a first preferred embodiment is shown thatschematically depicts various component parts of a jet engine protectionsystem and their relationships each to the other. The overall systempreferably includes a RADAR or LIDAR sub-system, which further includesa conventional antenna (not shown) and associated, conventionalmechanisms and circuits used to convey data signals to a digitalcomputer or processor sub-system (not shown). Commercially availableradars such as those available from Accipiter Radar Technologies, Inc.,a subsidiary of Sicom Systems Ltd., known as the Avian Radar DetectionSystem (AccipiterAR), or the DeTect Inc. Merlin Radar Detection Systemmay be used in the present systems. Commercially available LIDAR systemssuch as the Riegel BP560 or VQ480 product families may be used in thepresent systems.

Threat Evaluation Sub-Systems, Entire System Control and Algorithms

The processors for use in the present systems are digital computers andcorresponding computer-implemented software algorithms adapted tocontrol the operation of the entire system and to function as the threatlevel evaluation sub-system. It is believed that conventional computersand algorithms such as those used in the AccipiterAR System, the DeTectInc. Merlin, or the Traffic Collision Avoidance System (TCAS) (originaland improved versions) can be employed, with relatively minoradaptations to provide the processing functionality and features of thepresently described systems. Specifically, the TCAS system forintra-formation control as described in European Patent Specification EP1,147,506 B1, hereby incorporated by reference, exemplifies such aconventional system. Specifically regarding the computer implementedsoftware or code for implementation of the presently described systems,the basic code or algorithm is commercially available and operating inthe TCAS system. In its second generation, TCAS II, such software iscommercially available from Rockwell Collins, as its ACSS (AviationCommunication & Surveillance Systems) product and from HoneywellAerospace as its “CAS 100” product. It is believed that the TCAS systempresently being developed referred to as “TCAS III”, can also readily beadapted for use in the presently described systems. Also, thecomputational algorithms as used on the AccipiterAR System, or theMerlin Radar Detection System, combined with that used in the TCAS asdeveloped in conjunction with the MITRE Corporation may be used. It isenvisioned that adaptation of the computational algorithms to determinewhether the size of the bird is sufficiently large that actuation of thedefensive mechanism(s) is required, and to control automatic actuationof the active members of the defensive mechanism(s) is within theordinary skill of this art.

Mechanical Deflection Sub-Systems

The first preferred mechanical embodiment or sub-system includes a setof streamlined rods or tubes spaced evenly around the circumference ofthe nacelle lip at its forward or leading end. They are preferablyhoused in the engine nacelle cowling, center hub, or aircraft fuselagestructure, and can be actuated to instantly deploy directly in front ofthe engine. When deactivated, this embodiment can be stowed by returningto its original configuration positioned inside the engine nacellecowling, center hub, or aircraft fuselage structure. These rods areintended to function to deflect the incoming avian threat away from theengine or to fragment the carcass to a size that does not threaten heengine. The rods or tubes are preferably streamlined and evenlydistributed around the circumference of the nacelle. When deployed theymeet at or near a single point in front of the engine. The rods arestowed in a retracted position in the front of the engine nacelle, andare actuated forward when a bird impact is imminent. Once the birdthreat has subsided, the rods are retracted back into the nacelle topermit unobstructed airflow to enter the engine.

The rods are preferably deployed in either of two ways: first, by amechanical actuation device driven by a motor; or second, by apyrotechnically actuated device. It is envisioned that the pyrotechnicaldevice will require less mass and will be easier to integrate into theaircraft nacelles. In order to deploy straight forward toward the frontof the engine, a damped pyrotechnic actuator would ignite in order topush the rods through a set of guide holes. The guide holes wouldfunction to ensure alignment. The system would also be constructed sothat the guide holes would force the leading ends of the rods to meet orcome close to meeting at a common vertex. The deployment time would beon the order of one second.

Detailed analysis of bird impacts can be found in the academicliterature. In many studies, the bird has been modeled as a soft bodyand treated as either a uniform fluid, such as water, or as a mass withvariable density, such as water with air bubbles. To estimate the forceswhich the cone of rods or tubes might experience during a bird impact,one can consider a bird colliding with a single tube, and at the tube'smidpoint so as to present the worst case scenario. When the birdcollides with the rod, the rod experiences a near-instantaneous shockpressure followed by a stagnation pressure. Both events together last atotal of only a few milliseconds. For the nominal case of an 8-10 poundbird on a collision course with a 747, the collision event can beexpected to last six milliseconds. Based on experimental data, the shockpressure for this case would be on the order of 275 MN/square meter andthe stagnation pressure 30MN/square meter. Assuming that the bird-tubeimpact area is 4 square inches (about 26 square centimeters), thistranslates to a force of 0.715 MN during the shock event (which lasts onthe order of 1 millisecond) and 0.078 MN for the stagnation periodfollowing the shock. A titanium tube was considered to undergo theimpact event at its midpoint. The deflection at the midpoint waspredicted to be 0.6 inch. This model did not take into account thepossibility of the bird splitting in half. The tube had a nominal 4-inchdiameter and a wall thickness of 1-inch, which is conservative. Themodel assumed that the bird impacted the tube and came to a completestop. Further, this model was based on a tube of circular cross-section.With reference to FIGS. 6A and B, a biconvex or airfoil-shapedcross-sectioned tube or rod would sustain less force upon bird impactand would exhibit greater strength in the impact direction.

In one preferred embodiment the cone of rods or tubes is augmented withadditional structural members near the nacelle lip. These membersmitigate the possibility of an ingestion in this region, where the rodspacing may exceed the dimensions of the bird's body, thus leaving ahole big enough for the bird to slip through. These additional memberswould initially deploy with the parent rods and then be folded outwardusing a spring. One such configuration envisions shaping for the rodssuch that each rod would have a diamond-like shape in cross-section, andwith two sharp corners and two rounded corners. The rod, as thusconfigured, therefore would have two sharp edges, like a sword, toensure that the bird will be split into two pieces, or more depending onwhere the impact occurs.

When stowed the members or rods reside in the front portion of theengine nacelle. In one preferred embodiment, upon receipt of a controlsignal for actuation, gases generated by small explosive charges propelthe ring forward to push the rods out of the nacelle. The ring is guidedby linear bearings and moves on a path parallel to the engine shaft,that is, its longitudinal axis. A fixed ring is also mounted inside thenacelle close to the inlet lip and functions to guide the rods or tubesduring the deployment step. Holes in the ring serve to orient the rodsforward and towards the hub. The rods, tubes or other shaped membersmeet at or near a point, forming a cone. At the base of the coneadditional rod-like members form a lattice which protects the outerannulus of the engine intake area. The members of this lattice attach tothe primary rods and to the nacelle lip. When the device is to beretracted, the nacelle lip attach points release the secondary rods. Thering to which the primary rods are attached is winched back into itsoriginal location in the nacelle via a cabled pulley system with therods being guided by the guide holes in the front of the nacelle alsoreturn to their stowed position. The terms used to describe thisalternate embodiment have their ordinary meaning as would be commonlyunderstood in this field and it is believed that construction of thisembodiment is within the ordinary skill of this art.

In another preferred embodiment an inflatable bag is provided andadapted to be deployed in front of the engine. The bag would be deployedand inflate rapidly in much the same manner as automobile airbags. Also,as with the cone of rods embodiment, the airbag embodiment would beactuated by the threat level evaluator sub-system. Because of anairbag's comparatively greater impact on airflow into the engine, it isdesirable to minimize the duration of the deployment, that is, toactuate retraction as soon as possible once the bird has been deflected.Two embodiments or approaches are preferred for deployment, and they arecontingent on the precision with which the bird's location can bedetermined. It is believed that a bird's location, once tracked by thesensor sub-system, may be known only to within a radius of a few meters.To reduce this uncertainty a dual sensor sub-system would be used. Insuch a usage a primary, nose mounted sensor would sweep the airspace infront of the plane and would be used to determine onto which side of thefuselage the bird it likely to impinge. Following this determination, asecond, or last-second triggering sensor located on the presumed impactside would confirm the bird's approach to that side and subsequentlydeploy the airbag at the appropriate engine.

Alternatively, if the trajectory of the incoming threat, presumed to bea bird, relative to the aircraft can be predicted by the evaluatorsub-system with relative high certainty, the airbag's deployment couldin theory be targeted to collide with the bird en route to the airbag'sreturn to a stowed configuration. In this context the term “airbag” isused broadly to refer to a flexible and/or inflatable member that couldperform the described function. Intercepting the bird at the correctinstant would greatly reduce the amount of time that the deployed deviceor member blocks the airflow into the engine.

Two shapes are envisioned for the airbag structures. One would have aminaret shape that could potentially deflect the bird and put it on apath around the nacelle, rather than through the engine. Another shapeis similar to that of the well-know Hershey's kiss candy drops, withflat end pointing forward from the engine and the pointed end attachedto the hub

These mechanical sub-systems are intended to operate on the modernhigh-bypass ratio turbofan jet engine; however, they could be used onthe turbojet engine as well. Additionally, the systems are not limitedto use solely on a jet engine; there are other aircraft types in whichthey can be utilized for protection against impact from birds.Specifically, they can be employed to protect the exposed, vulnerablecomponents of a helicopter rotor system against threats posed byrelatively large birds and other objects.

The presently described systems are intended to address major problemsthat have not been addressed by known aircraft engine protectionsystems. In those systems, typically some type of screen device ispermanently affixed in front of the engine. This causes at least twomajor problems for any jet aircraft engine: having to deal with unwantedeffects created by the very nature of the devices, such as for exampleice formation, and disruption of airflow into the engine which in turncauses significant and unacceptable reduction in engine performance. Thesolution presented here includes active members that are brought intooperation at the point of need to deal with a bird or object about tocollide with the engine, and are subsequently withdrawn or stowed orretracted after the need has passed. It is believed that embodimentsemploying these principles eliminates both of the above-describedproblems and leave routine engine operation undiminished by itspresence. Yet the presently described system embodiments are ready toperform at any time, without requiring action by the pilot or otherperson(s).

The preferred systems include an active defensive mechanical system,sub-system or unit, including an actuator sub-assembly and a defensivedevice that is adapted to engage incoming birds or other objects, andwhich may be in the form of several different, preferred embodiments.These systems are believed to be a prime solution for use on numerousjet-engine-powered aircraft, both turbojet and turbofan, as well as onhelicopters and VTOL/VSTOL/STOVL aircraft.

With reference now to the drawings, preferred embodiments of jet engineprotection systems, sub-systems and components will be described. Asshown in FIG. 1 aircraft 20 includes a first jet engine 22, second jetengine 24 and a sensor sub-system 26 mounted in the nose of theaircraft. The sensor sub-system 26 detects airborne obstacles in frontof the aircraft and sends data signals representative of the speed,size, range and direction of travel of the obstacles to an embeddedprocessor 28 which preferably runs real-time evaluative algorithms toprocess the sensor data. A defensive mechanism 30 is positioned on thefirst engine 22 and a second defense mechanism 32 is positioned onsecond engine 24. These defensive mechanisms may optionally be activatedor retracted by mechanical or explosive actuators 34, 36, respectivelyin response to control signal sent by processor 28 to each of theactuators 34, 36.

Also referring to FIG. 1, the processor 28 communicates with theaircraft's autopilot system 38 and cockpit display system 40 in order tobroaden the system's response to a detected airborne object, such as abird. Based on the computed threat level of the obstacle, the embeddedprocessor 28 will transmit control signals to actuate mechanisms 34 and36, to alert the pilot via display 40, and/or send a command signal toautopilot 38 to automatically maneuver the aircraft.

FIG. 1 represents these primary system elements in a schematic mannerfor one of the engines. The preferred system would be installed on allengines of the aircraft.

Referring to FIG. 2 a front view of a conventional, typical high-bypassratio turbofan jet engine illustrates the nacelle cowling 42, nacellehousing panel 44, nacelle lip 46 and engine blades 48. This type ofengine has a relatively large size of the inlet to be protected againstbird strikes or ingestion of other airborne objects as illustrated byshowing the man 52 standing inside of its air intake structure.

FIG. 3 shows a modern high-bypass ratio turbofan jet engine incross-section and with several components positioned in relation to thejet engine's center hub 50, the nacelle cowling 42 and the engine core54. The active components of the deflection device can be fixed orsecured, adhered, positioned and/or attached to the inside of theexisting structure of the nacelle cowling 42 or the center hub 50. Theseembodiments as well as other embodiments may provide for differentlocations for the active components and the other components indicated.Intake area 56 of the core of the engine is a region of increasedsensitivity to foreign object incursion, and thus requires increasedprotection relative to other areas of the engine.

Referring to FIG. 4 a preferred embodiment defensive sub-system is shownin which the active components 58 are housed in and circumferentiallyaround the engine nacelle cowling 42. These active components includescreens or guards made of rods or tubes of metal or other material andcan be provided in numerous forms and locations. They can be separateapparatus and/or secured or fixed, adhered and/or attached to thenacelle cowling and/or to the center hub 50 by various conventionalmethods. FIG. 4 shows the active components or members in theirretracted or stowed positions. FIG. 5 shows the active components intheir extended positions, forming a cone 60 that extends out in front ofthe engine. The active members and the nacelle cowling are structuredand adapted so that each of the active members form an arc such thattogether they form a cone with the distal ends of the active memberspreferably touching or nearly touching to form the tip of the cone at62. FIG. 6 illustrates the cone-shaped configuration of the activemembers in the extended position. Variation in length and curvature, aswell as cross-sectional shape may apply to the embodiments shown inFIGS. 4-6.

The active components of the defensive system are preferably blades,rods, tubes or metal members. A multiplicity of theseextensible-retractable metal shield shafts, rods, tubes or blades 58 arelocated around the periphery of the nacelle cowling 42 and shaped suchthat, on extending, preferably they will form a curved, slatted surfacein front of the engine face and will function to deflect or otherwisedestroy the oncoming bird(s) to such an extent that serious damage tothe jet engine is prevented.

As shown in FIGS. 5-6 the shafts/rods/tubes/blades 58 are in theiractive or extended position 60, such that all preferably touch eachother, or come close to touching each other at their apex on thelongitudinal centerline of the engine and thus function to preventbird(s) or foreign object(s) from entering the engine. With reference toFIGS. 6A and 6B an alternate configuration for the rods or tubes isshown. In this alternate embodiment the rods or tubes have a biconvexshape, a side view of which is shown in FIG. 6A and a cross-sectionalview of which is shown in FIG. 6B. The shafts/rods/blades can also takea lacing configuration and/or a longitudinal configuration as well ashaving a curved shape, for example, with the term “lacing” having itscommonly understood meaning in this field.

With reference to FIG. 7A, an alternate preferred embodiment is shown,and in which the active elements 59 are housed in the jet engine'scenter hub 50. FIG. 7A shows the positioning of these active components59 in their stowed or retracted positions within the center hub 50, withfan blade attachment (shown with diagonal lines, but not numbered) andnacelle cowling 42 for a typical modern high-bypass ratio turbofan jetengine. It is within the empty interior space of the center hub 50 thatthe active elements of this embodiment are housed. FIG. 7B illustratesthese active elements or members in their active or extended positions.These extensible/retractable members may be made of metal and in theshape of shafts, rods, tube or blades, preferably having the same orsimilar shapes, but not necessarily the same size or angular orientationas shown in FIGS. 4-6. They may be fixed, secured, adhered, positionedand/or otherwise attached within the center hub.

Referring to FIGS. 8-9 the airbag preferred embodiment of the presentjet engine protection system is shown. In the FIG. 8 embodiment thedefensive system's active element is preferably a high-strengthinflatable bag 64 having a relatively flat or blunt leading end 66 thattapers to a relatively narrow cross-section 68 where it joins the enginehub 50. The FIG. 9 embodiment bag 70 is shaped like a minaret, with itsleading edge coming to a point 72. The bags are preferably made of afabric that will function to deflect an incoming bird or other objectbut will not seriously damage the jet engine if ingested into theengine, such as for example, an aramid fabric or material, commonlyreferred to as “Kevlar”. In the stowed position the bags 64, 70 arefixed, secured, adhered, positioned and/or attached within the centerhub 50 of the engine. As shown in FIGS. 8-9, the inflatable bags areshown in their actuated position or inflated condition. Once the impacthas taken place, the bag is stowed, retracted or safely jettisoned.Also, various methods of securing, fixing, adhering and/or attaching tothe center hub may apply to the FIGS. 8-9 embodiments. Variation in sizeand shape of the actuated airbag may also apply to the FIGS. 8-9embodiments.

Referring to FIG. 10, a schematic or block diagram of a preferredembodiment of the sensor data processing software algorithm 74 and itsfunctional steps are shown. This software preferably functions tocontrol the protection mechanisms, without requiring intervention by ahuman operator. Based on detection and evaluation of the bird threat,the processing software emits a notification message to the cockpit andan “alert” signal to cause the mechanical sub-system to be actuated or,in other conditions to not be actuated if the threat does not imply acollision.

Searching the possible-hazard airspace in front of the aircraft is doneautomatically by initiating sensor scan 76, by both the LIDAR and theRADAR sub-systems 78 and 79, respectively. When the LIDAR sub-system 78signal indicates a return from the defined scan sector in which apotential threat could occur, there is the possibility that it is anactual object, shown at decision point 80.

If the software algorithm determines that there was no object, thesystem returns to scanning as before and as shown by line 82. If anobject is detected, then information from the RADAR subsystem 79, whichhas been operating simultaneously, is, as shown by line 84 sent toanother functional part of the algorithm and is used to compute thelocation of the target in space, illustrated at 86. This dual-sensorapproach exploits the precision azimuthal ability of the LIDAR 78 andcombines it with the high-resolution range information from the RADAR 79to provide a highly precise location of the target at 86.

The software then checks, at 88 to determine if the detected object iswithin a pre-determined danger zone. The danger zone locationinformation would be predetermined by conducting analyses thatinvestigate a wide range of parameters involved in the multiplicity ofsituations that could be anticipated, so that essentially all possibleaircraft/bird encounters would have been evaluated. Example variablesincluded would be: bird type, size and weight; bird flight speed andability to change direction in-flight; aircraft type, such as make andmodel; essential capture area of the specific engine(s) on the aircraft;aircraft position and attitude including current speed, altitude, rateof climb or descent, heading and heading change, maneuver limitations,especially limiting “g” forces, and any other information having abearing on a potential collision. If this check indicates that theobject is not presently evaluated to be within the danger zone, andtherefore does not pose an immediate threat to the engine(s), a signalis sent via line 90 to actuate an alert. The alert is sent to thepilot(s) because it is considered important to inform the pilot(s) ofthe possibility of a danger, and to make the pilot(s) aware of thepotentially dangerous situation. Pilot workload is high, especially soduring the flight segments when the preponderance of bird collisionsoccur, namely takeoff and landing. It is important to convey suchinformation to the pilot in a timely fashion, but it is also importantthat unnecessary information be strictly avoided. It is envisioned thatthe precise way in which this information will be conveyed will be theresult of a collaborative effort with government agencies and airlinecommunity participants. In the event the algorithm makes thedetermination at 88 that the object is not in the danger zone, an alert,shown at 92 would be communicated to the pilot(s). The alert preferablywould include a caution indicator light on the cockpit panel and/or anaural warning to the pilot(s), with a statement, for example: “Possiblehazard detected at XX azimuth, YY elevation. Check visually”, with thesystem automatically stating the actual azimuth and actual elevation ofthe object. At this point in the evaluation of available information,there is always the possibility of a false alarm, so the specificlocation and color of the caution indicator within the cockpit and thewording of the aural warning would be carefully determined. Once thealert is sent to the pilot(s), or simultaneously with sending the alert,the algorithm signals, via line 94, the system to return to scanning at76.

Returning to the calculation shown at 88, if the object detected isdetermined to be within the pre-determined danger zone, the algorithmdirects, as shown by line 96, the LIDAR sensor to aim and search in thevicinity of the detected object, where it re-scans the region ofinterest, as shown at 98. If time permits, the sensor will scan twice ormore, and the computer implemented software will compute an estimate ofthe bird's trajectory. Output from the LIDAR will indicate either arepeated detection or no further detection, as shown at 100. If in thisperiod an object is no longer detected, this information is conveyed, asshown by line 102 to the pilot(s). In this situation, the pilot(s)should be informed as in the earlier instance, as described above inconnection with the alert represented at 92. At this point, the systemhas collected and processed additional information about the object,such as whether an increased likelihood of an actual possible collisionexists. The pilot(s) need(s) to be alerted of any such higher level ofconcern, so the specific information communicated to the pilot(s) wouldindicate any increased need for caution. As discussed above,collaboration with government agencies and the airline community woulddetermine the exact way to convey the information. Preferably, an auralwarning different than the one described above would be indicated, asshown at 104. For example the audible statement triggered at 104 couldbe: “Momentary LIDAR reading of possible hazard, no longer in field ofview”. Similarly, a different indicator light preferably would beselected. Following or simultaneous with actuating the warning, thesystem would signal, as shown by line 106 that scanning re-initiate orcontinue scanning as shown at 76.

Returning to the object detection function represented at 100, in thecase where the object has been detected again, system will signal, at108, the algorithm to use data from the LIDAR 78 and RADAR 79 sensors tocompute the object's velocity vector as represented at 110. Thisinformation is needed to calculate the precise trajectory or geometryfor a bird-to-aircraft collision. With the computation made at 110, thesystem will then compute a threat level by comparing the currentsituation with stored data, as shown at 112. These data will have beendeveloped by analyzing possible encounter situations and thendesignating, or pre-determining a set of categories of collisionlikelihood, for which parametric levels of threat would be assigned. Notall encounters will lead to a collision and thus the algorithm wouldmake a decision on whether the calculated threat is above apre-determined threshold, as represented at 114. If the threat leveldetermined is not above a tolerable threshold, the system will signal,via line 116, return to scanning at 76. If the threat level isdetermined to exceed the pre-determined, tolerable threshold level at114, the system then preferably will send a signal, shown at 118, togenerate an alert to the pilot(s) and automatically commence actuationof the engine protection device, as represented at 120. Also, if timedoes not permit—for example, if the bird is within a pre-defined zonetoo close to the aircraft to expend more time on data processing—then analert and/or actuation signal will be sent and the engine protectiondevice actuated automatically. As discussed above, collaboration amonggovernment agencies and the airline community will determine the exactvisual and verbal means by which to convey the information. Becausemultiple birds may be in the area, a signal, via line 122, will causethe system to continue to operate by continuing its scanning as shown at76.

Referring to FIGS. 11A and 11B, an alternative embodiment of theinflatable bag member is depicted as inflating bag 124 in FIG. 11A. Thebag 124 is mounted at two or more points 126 along the lip 128 of theengine nacelle 42. When a bird 130 approaches the engine, the folded,stowed bag 124 begins to be deployed from one side of the nacelle 42,the left side as shown in FIG. 11A. During deployment, pressurized airis forced into the bag via tubes 132 at the attachment point and the bagbegins to take on a more inflated form shown at 134 and begins to rotatein the direction of arrow 136. Referring to FIG. 12A, the bag is shownin its fully inflated position 138 intercepting the bird and “catching”it in a pocket of fabric at 140. The bag continues to move in anarc-like path in the direction of arrow 142 and removes the bird fromits collision path. The bird and bag may then be jettisoned, shown inFIG. 12B at 144 and downstream in the direction of arrows 146, 148 and150 and away from the engine at 152. Alternatively, with reference nowto FIGS. 13A and 13B if the bag 138 is secured in place and held firmlyat the attachment points 126, the bird may be held against the side ofthe nacelle 42 for the remainder of the flight as shown by arrows 154and 156.

Referring to FIG. 14, a frontal view of the inflatable moving bags ofFIGS. 11-13 is shown with the engine inlet in the background. The devicehas inflatable pockets, one of which is illustrated at 158. In FIG. 15,an isometric view of this device is shown.

Referring to FIGS. 16-18 an alternate embodiment adapted to provide adefensive system adapted for use with a helicopter 160 is shown. FIG. 16shows at location 162 the area in front of the helicopter blade controlmechanism. A preferred location for the defensive device or member atlocation 164 is shown in FIG. 17, with the active elements of the deviceshown in their stowed or retracted positions in FIG. 17 and in theiractive or extended position 166 in FIG. 18. This alternative embodimentpreferably employs the same type of system components as previouslydescribed with respect to the embodiment shown in FIG. 5, modified oradapted so that the metal shafts/rods/tubes/blades are positioned alongthe longitudinal centerline of the helicopter. When in their extendedposition they function to prevent bird(s) or foreign object(s) fromstriking the rotor control mechanism. The shafts/rods/tubes/blades canalso take a lacing configuration, as that term is commonly understood inthis field, and/or a longitudinal configuration as well as having acurved shape, for example.

Other alternative embodiments not illustrated include having the activecomponents or active member(s) made of resistive armor and shaped tofunction as defensive armor, or including a directed energy device, suchas a microwave transmitter that has the capability of transmitting abeam of sufficient intensity to destroy, deflect or injure the bird toprevent it from continuing on its collision course with the jet engine.Other alternate embodiments not illustrated and specifically adapted foruse on aircraft having jet engines mounted to the aircraft's fuselageinclude having the active components positioned or attached to thefuselage upstream or forward of the engine air intake, and uponactivation then extend outward in front of the engine to destroy thebird using blades or other solid members, or deflecting the bird using abag or bag-like structure.

Because many varying and different embodiments may be made within thescope of the inventive concepts herein taught, it is to be understoodthat the descriptions herein are to be interpreted as illustrative andnot in a limiting sense. Although specific embodiments of the inventionhave been described, various modifications, alterations, alternativeconstructions, and equivalents are also encompassed within the scope ofthe invention. The specification and drawings are, accordingly, to beregarded in an illustrative rather than a restrictive sense. It will,however be evident that additions, subtractions, deletions, and othermodifications and changes may be made thereunto without departing fromthe broader spirit and scope of the invention as set forth in theclaims.

1. A jet engine protection system for an aircraft comprising: a. asensor sub-system positioned on said aircraft, adapted to scan an areaof interest in front of said aircraft, adapted to detect a flying birdhaving a size greater than a predetermined size, adapted to detectwhether said flying bird is within a predetermined range of saidaircraft, adapted to generate bird characteristics signalsrepresentative of said flying bird and adapted to transmit said flyingbird characteristics signals to a digital processor; b. a threatevaluation sub-system comprising said digital processor and an algorithmimplemented in said processor, said algorithm adapted; (1) to evaluatesaid flying bird characteristics signals; (2) to evaluate aircraftflight characteristics signals of said aircraft while in flight; (3) todetermine a threat level associated with a risk of collision said flyingbird with said jet engine; (4) to determine whether said threat level isgreater than a predetermined threat level; (5) to generate controloutput signals if said threat level is greater than said predeterminedthreat level; and, (6) to transmit said control output signals to anactive defensive mechanism; c. said active defensive mechanism attachedon said aircraft and adapted to move from a retracted position to anextended position in front of said jet engine upon receipt of saidoutput control signals, and, wherein said active defensive mechanismincludes an inflatable bag made of an aramid mounted on said jet engineand adapted to extend from an un-inflated condition to an inflatedcondition upon activation of said defensive mechanism and then to extendmomentarily in front of said jet engine.
 2. The system of claim 1wherein said inflatable bag is anchored to said jet engine at twopoints, on approximately opposite sides of said jet engine.
 3. A jetengine protection system for an aircraft having a high-bypass ratioturbofan jet engine, said engine having a nacelle, a nacelle cowling,and a nacelle lip extending circumferentially around said nacelle,comprising: a. a sensor sub-system positioned on said aircraft, adaptedto scan an area of interest in front of said aircraft, adapted to detecta flying bird having a size greater than a predetermined size, adaptedto detect whether said flying bird is within a predetermined range ofsaid aircraft, adapted to generate bird characteristics signalsrepresentative of said flying bird and adapted to transmit said flyingbird characteristics signals to a digital processor; b. a threatevaluation sub-system comprising said digital processor and an algorithmimplemented in said processor, said algorithm adapted (1) to evaluatesaid flying bird characteristics signals; (2) to evaluate aircraftflight characteristics signals of said aircraft while in flight; (3) todetermine a threat level associated with a risk of collision said flyingbird with said jet engine; (4) to determine whether said threat level isgreater than a predetermined threat level; (5) to generate deploymentcontrol output signals if said threat level is greater than saidpredetermined threat level; (6) to transmit said deployment controloutput signals to an active defensive mechanism; (7) to generateretraction control output signals after transmission of said deploymentcontrol output signals and after said threat level is less than saidpredetermined threat level; and, (8) to transmit said retraction controloutput signals to said active defensive mechanism; and, c. said activedefensive mechanism comprising: (1) a set of streamlined rods housedinside of said nacelle cowling and spaced evenly about said nacelle lip;(2) an actuator adapted to deploy said rods out in front of said engineupon receipt of said deployment control output signals from said threatevaluation sub-system; (3) said rods configured and adapted to convergetoward a point in front of said engine upon activations by saidactuator; and, (4) said active defensive mechanism adapted to retractsaid rods back within said nacelle cowling upon receipt of saidretraction control output signals from said threat evaluationsub-system.
 4. A method for protecting a jet engine from ingestion offoreign objects, including large birds, said engine being mounted on anaircraft, said engine being a high-bypass ratio turbofan jet engine, andsaid engine having a nacelle, a nacelle cowling, and a nacelle lipextending circumferentially around said nacelle, comprising: a.providing a sensor sub-system positioned on said aircraft, said sensorsub-system: b. scanning an area of interest in front of said aircraftduring flight; c. detecting a flying bird in said area of interest andsaid bird having a size greater than a predetermined size; d. detectingwhether said flying bird is within a predetermined range of saidaircraft; e. generating flying bird characteristics signalsrepresentative of said flying bird; f. transmitting said flying birdcharacteristics signals to a digital processor; g. providing a threatevaluation sub-system comprising said digital processor and an algorithmimplemented in said processor, said algorithm: h. evaluating said flyingbird characteristics signals; i. evaluating aircraft flightcharacteristics signals of said aircraft during flight; j. determining athreat level associated with a risk of collision of said flying birdwith said jet engine; k. determining whether said threat level isgreater than a predetermined threat level; l. generating deploymentcontrol output signals if said threat level is greater than saidpredetermined threat level; m. providing an active defensive mechanismcomprising: n. a set of streamlined rods housed inside of said nacellecowling and spaced evenly about said nacelle lip; o. an actuator adaptedto deploy said rods out in front of said engine upon receipt of saiddeployment control output signals from said threat evaluationsub-system; p. said threat evaluation sub-system transmitting saiddeployment control output signals to said active defensive mechanismactuator when said threat level is greater than said predeterminedthreat level; q. said actuator causing said rods to move out of saidnacelle cowling and to converge toward a point in front of said engineupon receipt of said deployment control output signals from said threatevaluation sub-system; r. said threat evaluation sub-system generatingretraction control output signals after transmission of said deploymentcontrol output signals and after said threat level is less than saidpredetermined threat level; s. said threat evaluation sub-systemtransmitting said retraction control output signals to said activedefensive mechanism; and, t. said active defensive mechanism retractingsaid rods back within said nacelle cowling upon receipt of saidretraction control output signals from said threat evaluationsub-system.